Objective To solve frequent late frosts in spring and the mismatch of male and female flowering periods in walnut production, this study investigates the starting time of germination and flower period of 84 walnut germplasm resources in Qinhuangdao, Hebei, aiming to provide a reference for breeding late frost-resistant varieties, optimizing the arrangement of pollinator trees, and enhancing walnut yield.

Method In 2024, the starting time of germination and flower period of 84 walnut germplasm resources in Changli County, Qinhuangdao City, Hebei Province, were investigated, and atmospheric temperatures during this period were recorded. The effective accumulated temperature of ≥10 ℃ required for germination and flowering was calculated.

Results (1) The germination period of 84 walnut germplasm resources started from March 24 to March 31, requiring an average ≥10 ℃ effective accumulated temperature of 6.12 ℃; the peak period for male flowers started from April 17 to May 10, requiring an average ≥10 ℃ effective accumulated temperature of 103.69 ℃; the peak period for female flowers started from April 18 to May 15, requiring an average ≥10 ℃ effective accumulated temperature of 109.25 ℃. (2) The 84 germplasm resources were categorized into three groups: early-flowering group (April 17 − April 26), mid-flowering group (April 27 − May 6), and late-flowering group (May 7 and later). (3) In future walnut breeding work, we can select cultivars with late germination period such as ‘Zhonghe3hao’ ‘Xiluo7hao’ ‘Jinboxiang2hao’ ‘Jinboxiang4hao’ ‘Xilin1hao’ ‘Lvxiang’ ‘Jinxiang’ ‘Huasheng1hao’ ‘Zhonghe2hao’ to avoid the late frost in spring (≤0 ℃); and combine reasonably of cultivars with early, mid, and late flowers, such as ‘Lipin2hao’ (female early-flowering group) with ‘Xiling’ (male early-flowering group), ‘Lvling’ (female mid-flowering group) with ‘Xilin1hao’ (male mid-flowering group), ‘Small fruit black walnut’ (female late-flowering group) with ‘Black walnut’ (male late-flowering group) to improve the pollination rates and fruit setting rates.

Conclusion The findings of this research provide important basis for the effective development and utilization of 84 walnut germplasm resources, optimizing the arrangement of pollinator varieties,screening and breeding late frost-resistant varieties, predicting germination and flower period to implement preemptive frost prevention measures, and promoting increased production and efficiency in the walnut industry.